The positioning of work stages must be accurate, and such accuracy requires rigidity in the drive structure. In addition, the small size of writing beams and the large areas to be exposed in modern semiconductor work require high response rates, which in turn requires mechanical rigidity. In a modern electron beam lithography system, a two axis stage is used for positioning a silicon wafer under an electron beam window. The silicon wafer is coated with a resist which will be selectively exposed in a desired pattern by writing of the electron beam and movement of the stage. A computer program controlling two motors connected to two stages suitably positions the stages. Typically the silicon wafer must move two millimeters to a new position in about 50 milliseconds. Accurate performance can be achieved with a servo control system which has a five millisecond response time. One limit on response time is set by the mechanical resonance resulting from elasticity between the servo motor and the stage. The frequency of this response should be 500 hertz or greater to achieve the desired response time.
Thus there is need for a stage drive mechanism which is rigidly connected to the stage for rapid and accurate response.